1. Field of the Invention
The present invention relates to a device for determining a malfunction of an engine cylinder of an internal combustion engine.
2. Description of the Related Art
When a malfunction such as a serious misfiring occurs in an engine cylinder, the engine torque drops and imburst fuel is often discharged from the engine cylinder and leaks therefrom onto surrounding parts of the engine. Accordingly, it is important that a driver know of the malfunction, and deal with same at an early stage.
Japanese Unexamined Patent Publication No. 61-258955 discloses a device for determining a malfunction in an cylinder of a multicylinder engine. In this device an engine speed in the power stroke of each engine cylinder is detected, and the difference between the two engine speeds for two successive power strokes is calculated. When the difference is larger than a predetermined constant reference value, it is determined that a misfire has occurred in the engine cylinder with a delayed power stroke, and accordingly, a misfire count value is incremented by "1". The routine is carried out a predetermined intervals, and when the misfire count value becomes larger than a predetermined malfunction determining value, it is determined that a malfunction has occurred in the engine cylinder.
In the above device, the predetermined constant reference value is made relatively small, to thereby determine a misfire without fail under all engine driving conditions. Therefore, according to an engine driving condition, the difference can be larger than the predetermined constant reference value even though a misfire has not occurred, and thus the misfire count value becomes larger than the predetermined malfunction determining value, and accordingly, it is determined that a normal functioning cylinder is a malfunctioning cylinder.